1. Field of the Invention
The present invention is directed to the recovery of triarylboranes and more particularly to the separation of triphenylborane from diphenyl borinic acid by conducting the neutralization to a specified pH in a solution having a specified ionic strength.
2. Description of the Prior Art
Organoboranes have been produced by a variety of methods including the Grignard reaction and more recently by the reaction of an alkali metal, an organohalide and an orthoborate ester. Although the prior discloses many processes for the preparation of the substituted boron compounds, the prior art does not suggest efficient methods to obtain relatively pure trisubstituted boranes in good yield when significant amounts of other substituted boranes are present.
U.S. Pat. No. 3,090,801 issued on May 21, 1963 to Washburn et al. discloses processes which purport to produce mono, di and trisubstituted boranes in high yields but the patentee's only disclosure of a method for recovery of the boranes is found in the examples. In Example 1 of the patent, the reaction mixture is treated with methanol and water to hydrolize the dimethylboronate to produce the acid form. After the acid form is obtained, the mixture is then distilled to remove xylene, methanol and side reaction products. In Examples 2 and 3, the patentee purports to recover the acid form of the borane by contacting the reaction product with an aqueous solution containing concentrated sulfuric acid followed by extraction or distillation. These recovery procedures are not satisfactory for the trisubstituted boranes because the trisubstituted boranes are relatively unstable and readily degrade in the presence of water and/or acid especially at elevated temperatures.